Learn Functions in Python Programming

Function (1) 1

Objectives O This chapter introduces: 1. Introduction to a function Writing a function Scope of variables in a function 2. 3. 2

Function O Function is an independent program block that can perform specific code O The program can call the defined function to execute the specified program O The code of the function can be reused and is easy to maintenance 3

Function O A function is defined using the def keyword O The code in the function needs to be separated from other programs by indentation O To call a function, use the function name followed by parenthesis The keyword to define a function function_name() def MyFunction(): ''' Function content ............ ' #The indented blocks are function content of MyFunction() #Use the function name() to call the function 4

Function O When the main program calls a function, the code in the function will be executed O After completing the execution of the code in the function, the function result will be sent back to the caller def SayHello():#the function needs to be defined before calling print('Hello') print('Good morning!') The indented block includes function content Program output: print('Hi.') SayHello() print('Nice to meet you.') 5

Function O Function can also declare variables, such as integer, floating-point number, or string The keyword to define a function function_name() def show_num(): a = 1 while a <= 16: print(a, end=' ') a *= 2 print() #The main program show_num()# Call the function show_num() # Call it again The indented block includes function content Program output: 6

Function import time #the main program while 1: period = time.strftime('%p') if period == 'AM': print(time.strftime('Am %I hour %M minute %S second')) else: print(time.strftime('PM %I hour %M minute %S second')) time.sleep(1) import time #the function def get_time(): period = time.strftime('%p') if period == 'AM': print(time.strftime('Am %I hour %M minute %S second')) else: print(time.strftime('PM %I hour %M minute %S second')) #the main program while 1: get_time() time.sleep(1) The left and the right program have the same functionality 7

Local variable O Any variable present outside any function block is called a global variable O Its value is accessible from inside of any function O The variable declared in the function is a local variable O This variable can only be used in the function O After the function is completed, the local variable will be disappeared def foo(): a = 10 print(a) foo() print(a) 8

Local variable a = 1 b = 2 def foo(): #a += 2 #UnboundLocalError: the local variable 'a' referenced before assignment a = 2 #the variables in Function will not replace the #variables in main program print('1. a=' + str(a) + ' b=' + str(b)) a += b print('2. a=' + str(a) + ' b=' + str(b)) Because the function does not declare any variable accesses the global variable b b, it Output result foo() print('3. a=' + str(a) + ' b=' + str(b)) If we assign another value to a globally declared variable inside the function, a new local variable is created in the function's namespace. This assignment will not alter the value of the global variable. 9

Global variable O If you need to access and change the value of the global variable from within a function, this permission is granted by the global keyword a = 1 b = 2 def foo(): global a #Specify a as the global variable a = 2 print('1. a=' + str(a) + ' b=' + str(b)) a += b print('2. a=' + str(a) + ' b=' + str(b)) Output result: foo() print('3. a=' + str(a) + ' b=' + str(b)) 10

Source O References: O https://docs.python.org/3/library/functions. html O Python 11

Exercise 1 O Design a program that will determine if the number inputted by the user is a prime or not. In addition, it will also ask the user to see if all factors of the inputted number is listed or not. The details can be seen in the example. Output example: 12

Exercise 2 O Write a program that accepts a sentence as input, and prints the numbers of letters and digits of the sentence on the screen. O Input: hello world! 123 Output: The number of letters is: 10 The number of digits is: 3 13

Exercise 3 O Write a program that will read the data from input.txt and ask the user to input a number N. If the number N is not listed in the input.txt, it will print -1; otherwise, it will print how many numbers listed in the input.txt less than N. O Input: Output: 11 22 -1 3 14